NIH funded researchers at The University of Tennessee Health Science Center currently have critical need for a flow cytometer with a minimum of five fluorescence channel detection, UV laser excitation, and autosampling capability. This application is for funds to purchase the Becton-Dickinson LSR flow cytometer, which is ideally suited to meet those demands. There are currently several flow cytometers in operation on the UTHSC campus. None of those flow cytometers is equipped with a UV laser. Only one instrument currently on the campus is capable of detecting five fluorescent channels; however, that instrument is dedicated for cell sorting and lacks the necessary detection sensitivity required for some investigators. The flow cytometer dedicated for cell sorting is not equipped with a UV excitation laser. All of the other flow cytometers currently available are limited to four fluorescent channels and are either inaccessible to the investigators in this application or are operating at near maximum capacity. Since its inception in the late sixties and seventies, flow cytometry has become a mainstay for almost all research that involves the analysis of cells and cell functions. Monoclonal antibodies to the plethora of cell membrane markers, differentiation markers or CD antigens, and probes for cytoplasmic constituents such as endosomes and lysosomal proteins have made flow cytometry an even greater research resource. Fluorescent dyes such as Indo-1 that changes its emission spectrum upon binding Ca2+ provide critical tools to analyze signaling through cell-surface receptors. The uses of flow cytometry by the investigators in this application include detection of macrophage ingested bacteria, detection of viral binding to cell-surface receptors, multiparameter analysis of cell surface markers on lymphocytes, quantification of Ca2+ mobilization to measure signaling in selected cell populations, measurement of gene expression using multiple GFP, and detection of membrane fusion using fluorescent markers.